The present invention relates, in general, to the field of magnetic data transducers and methods for producing the same. More particularly, the present invention relates to a process for producing a pole-trimmed writer in a magnetoresistive ("MR") read/write head, and a data transducer produced thereby, of especial utility in conjunction with shared, or merged, shields on magnetoresistive read heads.
Magnetoresistive heads, or sensors, are known to be useful in reading data from a magnetic surface with a sensitivity exceeding that of inductive or other thin film heads. In operation, an MR sensor is used to detect magnetic field signal changes from a magnetic surface due to the fact that the resistance of the MR sensor changes as a function of the direction and amount of magnetic flux being sensed.
Currently, the magnetic field signal changes encoded on the magnetically hard surface of a computer mass storage medium which are to be "read" by an MR read head are "written" by an associated write head, or writer. In those instances when the MR read head has associated shield layers, as described in the aforementioned patents and patent applications for example, the write head may utilize the top shield as a bottom pole producing what is known as a merged, or shared shield/pole structure.
In these combined read/write data transducer structures, it has been shown that the area of greatest magnetic flux in the shared shield/pole may move around within that layer from the area immediately beneath the upper pole of the write head adjacent the intermediate dielectric gap layer. In parametric terms, the write track may "wander" and fringe fields might result wherein a write operation may actually take place toward the side of a given track that might then erroneously be read as data from the adjacent track. Reduction of track wander and associated fringe fields is increasingly important as track spacing is decreased in an attempt to increase the areal density of a magnetic computer mass storage device.
As a consequence, it has previously been proposed to remove portions of the upper surface of the shared shield/pole surrounding the upper pole and gap layer by, for example, "notching" or "pole-trimming" the shield/pole by ion milling (using the upper pole as a mask), to reduce its width to an area equivalent to the upper pole to better confine the flux to the desired region. However, due to the fact that the shield may have to be milled down on the order of about a micron (".mu.") or more to effectuate the desired flux constraint, a typical ion milling operation could conceivably take on the order of 60 minutes or longer of device processing time. This protracted ion milling of the shared shield/pole and upper pole surface may result in potentially damaging heat build up in the device structure during the process and it has been found that the resultant slope of the surface achieved in this manner may be, for the most part, too long and therefore ineffective in confining the magnetic flux as needed.
Moreover, due to removal of this relatively large amount of shield, pole and gap layer material during the milling process, a significant amount of it will subsequently get re-deposited throughout the processing system and ultimately build up on the sides of the upper pole, the gap material and the lower "trimmed" pole further degrading device function. Build up of thickness of approximately one half of the thickness of the ion milled gap, shield and pole material has been typically observed. This is particularly true in the case of merged shield elements used in conjunction with MR read heads wherein the lower pole/shield is substantially wider than the top pole (on the order of 30 times wider) thus exposing much more material to the ion milling process and, therefore, resulting in the unacceptable re-deposition of materials noted previously, in particular the metallic shield material. In conventional inductive thin-film heads, this same ion milling operation is generally much less of a problem in terms of undesired re-deposition due to the fact that the lower pole is generally only on the order of 1.5 .mu.m wider than the top pole in the first instance, thereby exposing less metallic material to ion milling.